There are numerous applications for identifying fluid media and/or products or substances contained in fluid media, such as for example detecting products or substances in a fluid medium, quality control, or compliance checking, etc.
In the state of the art, the publication “A high density multipoint LAPS setup using VCSEL array and FPGA control” Sensors and Actuators B154 (2011), pp. 124-128, discloses a sensor known by the acronym L.A.P.S. (for light-addressable potentiometer sensor), of structure that comprises a potentiometer transducer in contact with the liquids for analysis and separated from a semiconductor element by an insulator. A modulated light source is used to create localized photon excitation that penetrates directly into the interior of the semiconductor element in order to generate electron-hole pairs in said element. A bias voltage applied to the terminals of the sensor leads to a photocurrent being generated. The value of the photocurrent depends in particular on the bias voltage, on the photon excitation, and on the potential of the interface between the liquid and the insulator.
It stems from the principle on which that sensor is based that the photocurrent signal is of a photocapacitive nature because of the interface between the insulator and the semiconductor. As a result, the sensitivity of such a sensor is low and the detected signal is of low power. Furthermore, it is found that the zones that are not lighted have an influence on the signal created by the localized zones that are lighted.
Also known in the state of the art is the publication “Chemical sensors for electronic nose systems”, Microchim. Act 1.49, pp. 1-17 (2005), which discloses an electronic nose system using a chemical sensor for analyzing volatile organic compounds. Such a system has a metal oxide semiconductor field effect transistor (MOSFET). The grid of the transistor is in contact with the gas for analysis and is separated from the drain-source junction by an insulator. Charges on the insulator influence the drain-source current by means of a field effect and consequently influence the photocurrent picked up across the terminals of the transistor, thus enabling the gas for analysis to be characterized.
It stems from the principle of that electronic nose that the current signal between the drain and the source is modulated by the field effect via the interface between the insulator and the fluid. A drawback of that electronic nose lies in the need to have a specific grid in order to characterize gases selectively. In this respect, and by way of example, in order to be sensitive to compounds that are neutral, it is necessary to use specific catalysts so as to decompose the neutral molecules into charged elements. Another drawback of that electronic nose (from the point of view of technologically implementing it) lies in the need for the drain and the source of each transistor to be electrically insulated from the fluid for analysis. The spatial resolution of that device is defined and limited by the size of each transistor.
In the technical field seeking to determine the purity of semiconductor materials and examining the lifetimes of minority carriers, it is known to use a microwave measurement technique associated with a pulsed laser source. For example, in order to measure the lifetimes of minority carriers of a semiconductor substrate, Document WO 94/14188 proposes surrounding the semiconductor substrate with a passivation solution and subjecting it to a microwave source and to a pulsed light source in order to create photogenerated electric charges. The reflective microwave energy is detected, thus making it possible to measure the lifetime durations of the photogenerated electric charges. On the basis of that measurement, it is therefore possible to detect defects in the semiconductor substrate.